Recent results imply that the visual input for stabilizing eye movements such as optokinetic nystagmus (OKN) arrives through the accessory optic system nuclei and functionally and anatomically related pretectal nuclei. These nuclei also provide the visual input to the vestibulocerebellum, which is believed to adjust the gain and phase of the vestibulo-ocular reflex (VOR) to meet functional requirements and is involved in the suppression of the vestibulo-ocular reflex during fixation or pursuit. Anatomical studies show that one of the accessory optic nuclei, the nucleus of the basal optic root (nBOR, homologous to medial terminal nucleus or nucleus of the transpeduncular tract) receives its input from the displaced ganglion cells of the retina and sends efferents to the oculomotor nuclei and the vestibulocerebellum, as well as to the inferior olive, which in turn sends climbing fibers to the cerebellum. We propose to study the function of these pathways by several techniques. Single-unit recording from nBOR will reveal the optimal stimulus characteristics of both the inputs and outputs of this nucleus, and perhaps will show whether the oculomotor and cerebellar outputs differ. Stimulation of nBOR may help clarify the nature of its direct oculomotor output, both in terms of the muscles affected and the excitatory or inhibitory effect of activity in this pathway. Studies on normal animals of OKN, visually-evoked neck reflexes and visual effects on VOR will permit comparison both with the electrophysiologial findings and with the behavior shown by animals with lesions of nBOR, as well as giving a more complete picture of the several interacting systems that produce effective visual stabilization. This work may permit a better understanding of the disorders producing the several forms of congenital nystagmus as well as other deficits of oculomotor stabilization.